A microprocessor controlled high precision electronic digital thermometer is provided which is capable of producing highly accurate temperature readings while using relatively inexpensive components. A constructed embodiment of the invention takes the form of a low cost, hand-held unit having performance capabilities equal to the performance capabilities of expensive laboratory-grade bench-top electronic digital thermometers.
The digital thermometer of the present invention is of the same general type as the digital temperature indicator system disclosed in U.S. Pat. No. 4,713,783 which issued Dec. 15, 1987 in the name of the present inventor. As in the system described in U.S. Pat. No. 4,713,783, the digital thermometer of the present invention uses a thermistor probe to obtain highly accurate temperature measurements which, in the case of the thermometer of the present invention, may be obtained over an extended temperature range.
In both systems, the thermistor probe controls a Wheatstone bridge which produces an analog signal when the thermistor probe causes the bridge to become unbalanced from a null point as the thermistor in the probe senses different temperatures. The analog signal from the bridge is converted into digital signals which are processed to control an appropriate temperature reading display.
Electronic digital thermometers are also described in U.S. Pat. No. 4,536,851 which issued Aug. 20, 1985 in the name of Germanton et al.
The electronic digital thermometer of the present invention is constructed in a manner such that while using relatively inexpensive stable resistors in the bridge, highly accurate temperature readings may be obtained, thereby obviating the need for expensive high precision resistors in the bridge such as required by the prior art high accuracy electronic digital thermometers.
The electronic digital thermometer of the present invention also has the feature in that it may be calibrated quickly and easily to exhibit extreme accuracy.